Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Another goal of semiconductor manufacturing is to produce semiconductor devices with adequate heat dissipation. High frequency semiconductor devices generally generate more heat. Without effective heat dissipation, the generated heat can reduce performance, decrease reliability, and reduce the useful lifetime of the semiconductor device.
FIG. 1a shows a conventional semiconductor package 10 with a semiconductor die 12 having an active surface 14. Bumps 16 are formed on contact pads 18 on active surface 14. Semiconductor die 12 is mounted to substrate 20 with bumps 16 electrically connected to conductive traces 22 on the substrate. Bumps 24 are formed on conductive traces 22 opposite semiconductor die 12. An underfill material 26 is deposited between semiconductor die 12 and substrate 20.
A thermal interface material (TIM) 30 is formed over back surface 28 of semiconductor die 12. A heat spreader or heat sink 32 is positioned over and mounted to TIM 30 over back surface 28 of semiconductor die 12, as shown in FIG. 1b. The pressure of mounting heat spreader 32 to TIM 30 forces a spreading or pump-out of TIM 30 from back surface 28 of semiconductor die 12. The pump-out of TIM 30 can also occur during power cycling and other conditions of thermal mechanical stress of semiconductor package 10. The pump-out of TIM 30 can create voids 34 in the TIM over back surface 28. The thinner coverage of TIM 30 over back surface 28, as well as the potential voids, reduces the thermal conductivity and efficiency of TIM 30 and heat spreader 32. The pump-out of TIM 30 can cause overheating and reduce the meantime between failures of semiconductor package 10.